For controlling the aerodynamic rudders modern aircrafts use the so called “fly-by-wire”-technology. The flight commands of the pilot are transformed by steering computers into electrical and/or optical signals, which are used for piloting actuators for hydraulically controlling the aerodynamic rudders. Furthermore, other devices inside an aircraft, like the landing gear or cargo compartment doors are hydraulically actuated. For operating such hydraulic systems powerful hydraulic pumps are necessary, which generally build up a working pressure, depending on a civilian or military use, between 150 bars and 400 bars. In general the hydraulic pumps are directly powered by the engines, wherein, as a side effect, acoustic vibration in a frequency range between about 200 Hz and 3.200 Hz are emitted of the hydraulic system.
For the abatement of such vibration phenomena in the hydraulic system, which results in many cases in an awkward noise disturbance of the passengers and which furthermore may lead to leakage, hydraulic dampers are applied where the hydraulic system is separated from a gas cushion, which functions restraining because of its elastic spring action, by a rubber membrane. In a known embodiment of such a damper element a perforated hollow cylinder acts as bearing for the rubber membrane. This construction holds the considerable disadvantage that in an inactivated state of the hydraulic system, when the operating pressure is about 0 bars, the complete pressure of the gas cushion acts always on the rubber membrane and presses it at least partially into the bores of the perforated hollow cylinder. Due to this effect the durability of the rubber membrane is reduced significantly, so that a frequent exchange of the rubber membranes is necessary with those damper elements, which leads to indefensible short maintenance intervals. Therefore, despite their outstanding damping action, dampers with gas-cushioned rubber membranes are not used in aircraft hydraulic systems at present.
The currently known embodiments of those damper elements are provided with a durability which is too short and accordingly with a maintenance intensity which is too high.